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outline 10
Comparative Physiology- Renner Lecture 10
| Question | Answer |
|---|---|
| rods use visual pigment called _________ | rhodopsin |
| what does rhodopsin consist of? | protein portion found in the membrane called opsin, and light absorbing component called retinal/retinene |
| what are 2 ways to increase surface area in rods? | 1. stacks or discs 2. microvilli within the discs |
| what causes a change in retinal? what kind? | light. conformational change |
| what happens when light hits? | conformational change that leads to the release of retinal from the opsin protein |
| what does the activation of rhodopsin activate? | it activates a regulatory protein called transducin |
| what is the function of transducin? | activates phosphodiesterase |
| _____________ dissociates from opsin which activates opsin | (trans) retinal |
| activation of rhodopsin activates a regulatory protein called ____________, which in turn, activates ___________ | transducin, phosphodiesterase |
| cGMP is transformed to 5' GMP (inactive form) by ___________ | phosphodiesterase |
| what does cGMP do at rest? | open Na+ channels that are found in outer segment |
| what channels does cGMP open? how many molecules per 1 channel? | chemically gated Na+ channel. 3 cGMP molecules to open 1 channel |
| the cell is kept in a depolarized state due to what? | Na+ channels being open |
| in the dark, there is no stimulus, therefore there is an/a_____________ of _______ | inward current, Na+ |
| dark current keeps Vm at ___________ which is ___________ positive than neurons. Which keeps Ca2+ channels open. Ca2+ stimulates _____________release | -40mV, more, neurotransmitter (glutamate) |
| what does phosphodiesterase do? | converts cGMP to 5'GMP, which is the inactive form |
| Na+ influx into the cell that keeps cell depolarized is also termed | dark current since there is no stimulus |
| dark current's effect on Ca2+ channels? | keeps them open |
| when Na+ channels don't recognize 5'GMP in the light reaction, what is the subsequent event? | K+ leaks out along its concentration gradient through non gated, passive channels found on inner segment to hyperpolarize the cell, decreasing NT release |
| ___________ of K+ hyperpolarizes the cell from _____ to _______ | leaking out, -40mv, -70mV |
| how will Ca2+ channels closing decrease NT release? | by stopping the docking sequence for exocytosis |
| how is transducin inactivated once light is removed? | by the hydrolysis of GTP on the molecule, leading to inactivation of rhodopsin |
| what are some visual adaptations in teleost fish? | 1. fusiform, eyes on sides-360 field 2. flat cornea-increase resistance to movement in h2o 3. lens large and spherical-light refraction, retractor muscle- back&forth 4. iris+pupil fixed diameter- light intensity slowly changes 5. color vision is common |
| why is the pupil and iris diameter fixed in teleost fish? what is an alternative? | light intensity changes slowly in water, no need to alter pupillary aperture. some fish change pigment when changing depth |
| how many cones does the mantis shrimp have? what does that tell? | 16 different types of cones compared to humans who have 3. it tells that color vision is common in deep water organisms |
| pupillary response to light is _________ in aqueous organisms | slow |
| refractory index of water is ____________ to the cornea of aqueous organisms , therefore most refractory power is found in the ____________ | similar, lens |
| function of tapetum lucidum ? | reflects light back on the retina |
| are there any glandular secretion in the eyes of aqueous organisms ? | no, since the eye is bathed with water there's no need for glandular secretion to clear the eye surface |
| what do glandular secretions do for terrestrial organisms? what is a different structure that has the same function? | keep the cornea moist and clean. The lids do that too. |
| major source of light refraction in terrestrial organisms is the ______________ because ______________________ | cornea, its refractive index is similar to air's |
| the ______________ is flat in terrestrial organisms, but in aqueous organisms the _________________ is flat | lens, cornea |
| the lens is located closer to the retina in terrestrial organisms, why? | to keep distant objects in focus |
| what are some adaptations nocturnal organisms have to achieve vision in dim light? | 1. large pupils-enhance light gathering 2. lens close to retina, spherical to improve refraction 3. cones sparse or absent 4. rods densely distributed, marked convergence on ganglion cells, enhance light sensitivity decrease acuity 5. tapetum lucidum |
| how is vision achieved in arthropods, and some mollusks? | compound eyes organized as individual units called ommatidia (ommatidium singular) |
| what is an ommatidium composed of? | two lenses, eight or more retinula cells-contain rhabdomere |
| what are rhabdomeres? where are they located? | photosensitive, pigment rich microvilli. located on edge of retinular cell facing center of ommatidium |
| outside of retinular cells is lined with what? for what purpose | pigmented cells to prevent light leakage |
| what are 2 major types of compound eyes?what is the difference ? | apposition and superposition. apposition ommatidium are optically isolated from each other and receive light from narrow visual field. superposition, each rhabdoms are separated from lenses by clear zone, each rhabdom receives light from multiple lenses |
| what are gains from each type of compound eye type? losses? | apposition: gain- increased visual acuity, loss- limit light gathering. superposition: gain- increase light gathering ability, loss- decrease visual acuity |
| apposition eyes are common in _________________ superposition eyes are common in ________________ | diurnal insects, nocturnal insects |
| invertebrates: light absorption--> open Na+ channels--> depolarize retinular cells. what is that mediated through? | second messenger system in which a G-protein activates an enzyme called phospholipase C |
| in invertebrates, function of phospholipase C? | breaks down a membrane phospholipid called phosphatidylinostiol biphosphate to form inositol-3P and diacylglyercol |
| in invertebrates, ___________ second messenger retinated in membrane following phospholipase C breakdown of PIP2 | DAG |
| in invertebrates, IP-3 is ____________ soluble and liberates ____________ into the cytosol from the _________________ | water, Ca2+, endoplasmic reticulum |
| in invertebrates, Ca2+ released into cytosol by IP-3 activates what? | Ca+/calmodulin dependent protein kinase |
| in invertebrates, in the presence of DAG, what does Ca2+ activate? | Protein kinase C |
| in invertebrates, what is the effect of the 2 protein kinases? | open Na+ channels to depolarize the cells |
| in invertebrates, Signal resulting from protein kinases depolarizing the cell is graded depending on what? | intensity of light absorbed |
| in invertebrates, how is depolarization transferred to the eccentric cell which transfer them to the brain? | through low resistance pathways known as gap junctions. |
| cell type in the invertebrate eye that conducts information in both direct (vertical) and lateral pathways | eccentric cell |
| structure in the insect eye that contains the photopigment rhodopsin | rhabdom of retinular cell |
| type of insect eye in which the ommatidia are optically isolated from each other | aposition |
| in invertebrates, what is meant by quantum bumps? | # of Na+ channels in response to 1000 Na+ channels per photon |
| what structure enables invertebrates of modifying signals in a lateral pathway? | eccentric cells and their ability to send collaterals to other surrounding eccentric cells that surround them |
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